Glass with reinforced layer and preparation method thereof

ABSTRACT

A glass with a reinforced layer is provided, including a glass body and the reinforced layer formed in a surface of the glass body. The compressive stress of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The compressive stress curve of the reinforced layer has an inflection point. The gradient of a first curve section in front of the inflection point is greater than the gradient of a second curve section behind the inflection point. The overall refractive index of the reinforced layer trends to decrease non-linearly from the surface of the glass body to the interior of the glass body. The refractive index curve of the reinforced layer has at least two inflection points. Furthermore, a method for preparing the glass with a reinforced layer is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 15/801,311 filed on Nov. 1, 2017, which is a ContinuationApplication of PCT Application No. PCT/CN2016/086517 filed on Jun. 21,2016, which claims the benefit of Chinese Patent Application No.201610428115.X filed on Jun. 16, 2016. All the above are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present application relates to the technical field of glassmanufacturing, and particularly to glass with a reinforced layer, and apreparation method thereof.

BACKGROUND

Chemically reinforced glass is currently widely used in mobile phones,media players and other terminals, due to its high transparency, highstrength and abrasion resistance. The high strength of the chemicallyreinforced glass is achieved by ion exchange. The principle is thatsmall ions in the glass can be replaced by the large ions in a moltensalt bath at high temperatures, and the large ions are tightly piled upon the glass surface to create a strong compressive stress afterreplacement, whereby a high strength is exhibited.

However, during the ion exchange process, the large ions in the moltensalt bath are diluted with increasing number of small ions exchangedout. If the same molten salt bath is still used, the compressive stressof the glass will be reduced. In order to solve such a technicalproblem, a solution is employed at present, in which the ion exchange isachieved with two different molten salt baths. The glass is initiallysubjected to ion exchange in a first molten salt bath, and then takenout, cooled and dried after the large ions in the first molten salt bathare diluted to some degree, preheated again, and then subjected to ionexchange in a second molten salt bath, where the concentration of thelarge ions in the second molten salt bath is greater than that of thelarge ions in the diluted first molten salt bath. The stressdistribution in the compressive stress layer formed by treatment withsuch molten salt baths is that the compressive stress layer does notchange much in the depth direction and the compressive stress layer hasa continuous monolayer structure. The concentration of the large ionsexchanged varies over the depth of the glass in such a pattern that theconcentration of the large ions is high merely at a position close tothe glass surface and declines sharply inside the glass. This willnecessarily result in uneven strength distribution of the compressivestress layer of the reinforced glass finally formed.

In short, so far, the stress distribution or the concentration of theexchanged ions in the monolayer compressive stress layer formed in theglass surface through physical or chemical tempering or through one ormore tempering processes decreases progressively along the directionfrom the glass surface to the interior of the glass, resulting in acompressive stress layer that does not change much in the depthdirection. As a result, the overall strength of the glass is failed tobe improved.

SUMMARY

Accordingly, the present application provides glass with a reinforcedlayer and a preparation method thereof, so as to enhance the internalcomposite compressive stress of the glass, thereby achieving anincreased overall strength of the glass.

Glass with a reinforced layer comprises a glass body and the reinforcedlayer formed in a surface of the glass body. The compressive stress ofthe reinforced layer trends to decrease non-linearly from the surface ofthe glass body to the interior of the glass body. The compressive stresscurve of the reinforced layer has an inflection point, and the gradientof a first curve section in front of the inflection point is greaterthan the gradient of a second curve section behind the inflection point.The overall refractive index of the reinforced layer trends to decreasenon-linearly from the surface of the glass body to the interior of theglass body, and the refractive index curve of the reinforced layer hasat least two inflection points.

Preferably, the reinforced layer contains metal ions exchanged into thereinforced layer, and the molar concentration of the metal ionsexchanged into the reinforced layer trends to gradually decreasenon-linearly in a direction running from the surface of the glass bodyto the interior of the glass body.

Preferably, a first inflection point on the refractive index curve ofthe reinforced layer is located at a position between 5-30 um in thedirection running from the surface of the glass body to the interior ofthe glass body, and located at a position reaching 4-50% of a totalion-exchange depth in the direction running from the surface of theglass body to the interior of the glass body. A second inflection pointis located at a position between 10-50 um in the direction running fromthe surface of the glass body to the interior of the glass body, andlocated at a position reaching 8-85% of the total ion-exchange depth inthe direction running from the surface of the glass body to the interiorof the glass body. A maximum value of the refractive index presents atan outermost surface of the glass body, and the difference between themaximum value and the refractive index of the glass body is not higherthan 0.1.

Preferably, the total ion-exchange depth is not less than 60 gm, and thecompressive stress at the surface of the glass body is not less than 600Mpa

Preferably, the reinforced glass has a thickness of 0.1-10 mm.

A method for preparing a glass with a reinforced layer comprises:

Step A: providing glass, preheating the glass in a temperatureenvironment lower than that of a molten salt bath, and subjecting thepreheated glass to a first ion exchange process for a time T₁ in themolten salt bath, to form a reinforced layer L₁ in a surface of theglass;

Step B: thermally processing the glass formed with the reinforced layerL₁ for a time t_(h) that is from above 20 min to 30 min in antemperature environment of T_(h) ranging from 390° C. to a temperaturethat is 10° C. below an annealing point of the glass, to allow theingredient of the molten salt bath adhered to the glass surface tofurther undergo ion exchange with the glass, and allow the reinforcedlayer L₁ to expand toward the interior of the glass by at least 3 gm,wherein the distribution of the ions exchanged into the reinforced layerL₁ is diluted, and a reinforced layer L₂ is formed by integrating theions newly exchanged in this step; and

Step C: cooling the glass having the reinforced layer L₂ to thetemperature of the molten salt bath, and subjecting the glass to asecond ion exchange process in the same molten salt bath in Step A; orrinsing the glass, and then subjecting the glass to a second ionexchange process in a molten salt bath different from that in Step A,where the time for the second ion exchange process is t₂, thetemperature for the second ion exchange process is T₂; and a reinforcedlayer L₃ is formed on the surface of the glass having the reinforcedlayer L₂ by ion exchange, the reinforced layer L₂ inside the glassundergoes ion exchange with the ions inside and peripheral to the glassand expands continuously toward the interior and periphery of the glassalong a direction of the concentration difference, the reinforced layerL₃ expands at a rate higher than that of the reinforced layer L₂, andafter full ion exchange reaction, the reinforced layer L₃ is overlappedwith the reinforced layer L₂, to form a reinforced layer,

where the time and temperature for the second ion exchange process inStep C and the time and temperature for the thermal processing in Step Bsatisfy T₂×t₂<T_(h)×(t_(h)/2).

Preferably, the glass having the reinforced layer L₁ obtained in Step Ais taken out, cooled, and rinsed, to remove the ingredient of the moltensalt bath adhered to the glass surface in Step A completely, and thenthe rinsed glass having the reinforced layer L₁ is used in the processof Step B.

Preferably, Steps B-C are repeated, until a satisfactory reinforcedlayer is formed in the glass.

Preferably, the temperature of the molten salt bath is 350-550° C.during the first and second ion exchange process.

Preferably, the glass is alkaline silicate glass comprising 15-72 wt %of SiO₂; 10-43 wt % of Al₂O₃ or/and P₂O₅ in total; 8-33 wt % of alkalinemetal oxides in total; and less than 15 wt % of other oxides.

Preferably, a maximum value of the refractive index presents at anoutermost surface of the glass body, and a difference between themaximum value and the refractive index of the glass body is not higherthan 0.1

Compared with the prior art, the present application has the followingadvantages.

In the preparation method according to the present application, acondition is established between the time and temperature for thethermal processing in Step B and the time and temperature for the secondion exchange process in Step C: T₂×t₂<T_(h)×(t_(h)/2). Glass with areinforced layer having characteristics different from those of thereinforced glass in the prior art is obtained through the preparationprocess where the condition is satisfied. Firstly, the refractive indexof the glass has unique features. That is, the refractive index of thereinforced layer trends to decrease non-linearly, on the whole, from thesurface of the glass body to the interior of the glass body, and therefractive index curve of the reinforced layer has at least twoinflection points. Secondly, the compressive stress distribution of theglass has its own features. That is, the compressive stress of thereinforced layer trends to decrease non-linearly from the surface of theglass body to the interior of the glass body; and the compressive stresscurve of the reinforced layer has an inflection point, the gradient of afirst curve section in front of the inflection point is greater than asecond curve section behind the inflection point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows distribution curves of K ions in molar percentage inreinforced layers obtained in different steps in an embodiment of thepresent application.

FIG. 2 shows distribution curves of the refractive index tested withpolarized lights in X and Y directions of glass with a reinforced layerobtained in an embodiment of the present application.

FIG. 3 shows a compressive stress distribution curve of glass with areinforced layer obtained in an embodiment of the present application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To make the objects, technical solutions and advantages of the presentapplication clearer, the present application will now be described infurther detail by way of examples with reference to the accompanyingdrawings. It is to be understood that the specific embodiments describedherein are merely illustrative of the present application and are notintended to limit the present application.

The present application provides a method for preparing glass with areinforced layer, which comprises the following steps.

Step A: Glass is provided, preheated in a temperature environment lowerthan that of a molten salt bath, and subjected to a first ion exchangeprocess for a time T₁ in the molten salt bath, to form a reinforcedlayer L₁ in a surface of the glass.

Step B: The glass formed with the reinforced layer L₁ is thermallyprocessed for a time t_(h) that is from above 20 min to 30 min in antemperature environment of T_(h) ranging from 390° C. to a temperaturethat is 10° C. below an annealing point of the glass, to allow theingredient of the molten salt bath adhered to the glass surface tofurther undergo ion exchange with the glass, and allow the reinforcedlayer L₁ to expand toward the interior of the glass by at least 3 μm,where the distribution of the ions exchanged into the reinforced layerL₁ is diluted, and a reinforced layer L₂ is formed by integrating theions newly exchanged in this step.

Step C: The glass having the reinforced layer L₂ is cooled to thetemperature of the molten salt bath, and the glass is subjected to asecond ion exchange process in the same molten salt bath in Step A; orthe glass is rinsed, and then subjected to a second ion exchange processin a molten salt bath different from that in Step A, where the time forthe second ion exchange process is t₂, and the temperature for thesecond ion exchange process is T₂; and a reinforced layer L₃ is formedon the surface of the glass having the reinforced layer L₂ by ionexchange, the reinforced layer L₂ inside the glass undergoes ionexchange with the ions inside and peripheral to the glass and expandscontinuously toward the interior and periphery of the glass along adirection of the concentration difference, the reinforced layer L₃expands at a rate higher than that of the reinforced layer L₂, and afterfull ion exchange reaction, the reinforced layer L₃ is overlapped withthe reinforced layer L₂, to form a reinforced layer; and the time andtemperature for the second ion exchange process in Step C and the timeand temperature for the thermal processing in Step B satisfyT₂×t₂<T_(h)×(t_(h)/2).

Optionally, the glass having the reinforced layer L₁ obtained in Step Ais taken out, cooled, and rinsed, to remove the ingredient of the moltensalt bath adhered to the glass surface in Step A completely, and thenthe rinsed glass having the reinforced layer L₁ is used in the processof Step B. The rinsing process before Step B is provided for preventingthe influence on the purity and the stress intensity of the finalreinforced layer by the ingredient of the molten salt bath that isreacted and attached to the glass surface during the thermal processingof Step B.

Optionally, Steps B-C are repeated, until a reinforced layer meeting thecompressive stress and depth requirements is formed on the glass.

During the preparation process, the temperature of the molten salt bathis 350-550° C.

By means of the preparation method, glass with a reinforced layer isobtained, which comprises a glass body and a reinforced layer formed ina surface of the glass body. The compressive stress of the reinforcedlayer trends to decrease non-linearly from the surface of the glass bodyto the interior of the glass body. The compressive stress curve of thereinforced layer has an inflection point, and the gradient of a firstcurve section in front of the inflection point is greater than thegradient of a second curve section behind the inflection point. Theoverall refractive index of the reinforced layer trends to decreasenon-linearly from the surface of the glass body to the interior of theglass body, and the refractive index curve of the reinforced layer hasat least two inflection points.

In the glass with a reinforced layer, the reinforced layer containsmetal ions exchanged into the reinforced layer, and the molarconcentration of the metal ions exchanged into the reinforced layertrends to gradually decrease non-linearly in a direction running fromthe surface of the glass body to the interior of the glass body.

In the glass with a reinforced layer, a first inflection point on therefractive index curve of the reinforced layer is located at a positionbetween 5-30 um in the direction running from the surface of the glassbody to the interior of the glass body, and located at a positionreaching 4-50% of a total ion-exchange depth in the direction runningfrom the surface of the glass body to the interior of the glass body. Asecond inflection point is located at a position between 10-50 um in thedirection running from the surface of the glass body to the interior ofthe glass body, and located at a position reaching 8-85% of the totalion-exchange depth in the direction running from the surface of theglass body to the interior of the glass body. A maximum value of therefractive index presents at an outermost surface of the glass body, andthe difference between the maximum value and the refractive index of theglass body is not higher than 0.1.

In the glass with a reinforced layer, the total ion-exchange depth isnot less than 60 μm, and the compressive stress at the surface of theglass body is not less than 600 Mpa.

The glass with a reinforced layer has a thickness of 0.1-10 mm.

The glass for forming the reinforced layer is alkaline silicate glasscomprising 15-72 wt % of SiO₂; 10-43 wt % of Al₂O₃ or/and P₂O₅ in total;8-33 wt % of alkaline metal oxides (Li₂O or/and Na₂O or/and K₂O) intotal; and less than 15 wt % of other oxides.

EXAMPLE

Molten salt bath: 100% KNO₃;

The time period and temperature for the first ion exchange process andthe time period and temperature for the second ion exchange processsatisfy: T₂×t₂<T_(h)×(t_(h)/2).

The temperature and time period for the first ion exchange process: 430°C., 3.5 h;

The time period and temperature for the thermal processing: 530° C., 2h;

The temperature and time period for the second ion exchange process:430° C., 1 h;

Component of the glass to be reinforced:

Component Content (wt %) SiO₂ 61 Al₂O₃ 17.3 Fe₂O₃ 0.5 CaO 0.2 MgO 3.2K₂O 1.8 Na₂O 15.5 TiO₂ 0.5

As shown in FIG. 1, after Step A is performed, a reinforced layer L₁ isformed on the surface and inside the glass, and the distribution of theexchanged ions K in molar percentage is as shown by the curve of thereinforced layer L₁ in FIG. 1. After Step B is performed, the glass isplaced in an environment where no source of ions for exchange isavailable, the K ions inside the reinforced layer L₁ can only be furtherexchanged with Na inside the glass, and the distribution of K expandstoward the interior of the glass on one hand, and is diluted on theother hand, thus forming a reinforced layer L₂. FIG. 1 shows adistribution curve of the exchanged K ions in molar percentage in thereinforced layer L₂. After Step C is performed, the reinforced layer L₂is redistributed again, and thus expands further toward the interior ofthe glass on one hand, and is further diluted on the other hand. As newK ions are exchanged into the glass from the molten salt bath containingthe source of ions for exchange, the K ions newly entered the glassmoves at a rate much faster than that of the existing reinforced layerL₂ in the glass, and is combined with the reinforced layer L₂, to form areinforced layer L₃. FIG. 1 shows a distribution curve of the exchangedK ions in molar percentage in the reinforced layer L₃.

Moreover, if a rinsing process is additionally added before Step B, andthe same conditions are maintained in the subsequent procedure steps,the resulting outcome can be slightly reflected in the curve of thereinforced layer L₂ and the curve of the reinforced layer L₃ obtained inSteps B and C respectively. The curve of the reinforced layer L₂obtained in Step B becomes slightly flattened, and the gradient will besmaller. The curve of the reinforced layer L₃ obtained in Step C alsohas the same characteristics of change. The change in the curve of thereinforced layer L₃ is very small, because a large amount of K ionsnewly entered the glass from the molten salt bath in Step C, and themolar concentration of these K ions masks the changes that present instep B. Therefore, although a rinsing process is added, thecharacteristics of the finally obtained reinforced layer L₃ areunchanged. The rising process is added for the purpose of removing theremaining ingredient of the molten salt bath on the glass surfaceobtained after Step A before it entering the thermal processing process(e.g. baking) of Step B, so as to avoid the destruction on the purity ofthe finally obtained reinforced layer L₃ by the remaining ingredient ofthe molten salt bath that is reacted upon heating and attached to theglass surface during the thermal processing of Step B, and avoid thecontamination of the molten salt bath used in Step C arising therefrom.

As shown in FIG. 2, the refractive index of the reinforced glass havingthe reinforced layer L₃ prepared through the method above has thefollowing characteristics.

When the stress is measured by an optical method, the refractive indextested with two polarized lights are obtained, and then the surfacestress is calculated according to the difference therebetween andaccording to various constants and variables of the glass and themeasuring instrument. The test method is within the prior art of theindustry, and will not be described again in the present application.FIG. 2 shows distribution curves of the refractive index tested withpolarized lights in X and Y directions of glass with a reinforced layerobtained in this example. Two refractive index distribution curves arecorrespondingly obtained. Apparently, FIG. 2 obviously shows that therefractive index of the reinforced layer L₃ trends to decreasesnon-linearly, on the whole, from the surface of the glass body to theinterior of the glass body, and the refractive index curve of thereinforced layer L₃ has at least two inflection points.

As shown in FIG. 3, the compressive stress of the reinforced layer L₃has the following characteristics.

It is known in the art that the compressive stress is obtained throughcalculation based on the values of the refractive indices measured atselected points and on other constants and variables introduced, andthen fitting a final curve. The method of fitting a curve is within theprior art of the industry, and will not be described again in thepresent application. Apparently, FIG. 3 obviously shows that thecompressive stress of the reinforced layer L₃ trends to decreasenon-linearly from the surface of the glass body to the interior of theglass body; and the compressive stress curve of the reinforced layer L₃has an inflection point, and the gradient of a first curve section infront of the inflection point is greater than a second curve sectionbehind the inflection point.

Compared with the prior art, the present application has the followingadvantages.

In the preparation method according to the present application, acondition is established between the time and temperature for thethermal processing in Step B and the time and temperature for the secondion exchange process in Step C: T₂×t₂<T_(h)×(t_(h)/2). Glass with areinforced layer having characteristics different from those of thereinforced glass in the prior art is obtained through the preparationprocess where the condition is satisfied. Firstly, the refractive indexof the glass has unique features. That is, the refractive index of thereinforced layer trends to decrease non-linearly, on the whole, from thesurface of the glass body to the interior of the glass body, and therefractive index curve of the reinforced layer has at least twoinflection points. Secondly, the compressive stress distribution of theglass has its own features. That is, the compressive stress of thereinforced layer trends to decrease non-linearly from the surface of theglass body to the interior of the glass body; and the compressive stresscurve of the reinforced layer has an inflection point, the gradient of afirst curve section in front of the inflection point is greater than asecond curve section behind the inflection point.

The foregoing description is merely illustrative of the preferredembodiments of the present application and is not intended to limit thepresent application. Any modifications, equivalent replacements andimprovements made without departing from the spirit and principles ofthe application are encompassed in the protection scope of the presentapplication.

1. A method for preparing a glass with a reinforced layer, comprising:Step A: providing glass, preheating the glass in a temperatureenvironment lower than that of a molten salt bath, and subjecting thepreheated glass to a first ion exchange process for a time period T₁ inthe molten salt bath, to form a reinforced layer L₁ in a surface of theglass; Step B: thermally processing the glass formed with the reinforcedlayer L₁ for a time period t_(h) that is from above 20 min to 30 min inan temperature environment of T_(h) ranging from 390° C. to atemperature that is 10° C. below an annealing point of the glass, toallow the ingredient of the molten salt bath adhered to the glasssurface to further undergo ion exchange with the glass, and allow thereinforced layer L₁ to extend into the interior of the glass by at least3 μm, wherein the distribution of the ions exchanged into the reinforcedlayer L₁ is diluted, and a reinforced layer L₂ is formed by integratingthe ions newly exchanged in this step; and Step C: cooling the glasshaving the reinforced layer L₂ to the temperature of the molten saltbath, and subjecting the glass to a second ion exchange process in thesame molten salt bath in Step A; or rinsing the glass, and thensubjecting the glass to a second ion exchange process in a molten saltbath different from that in Step A, wherein the time period for thesecond ion exchange process is t₂, and the temperature for the secondion exchange process is T₂; and a reinforced layer L₃ is formed on thesurface of the glass having the reinforced layer L₂ by ion exchange, thereinforced layer L₂ inside the glass undergoes ion exchange with theions inside and peripheral to the glass and extends continuously intothe interior and a periphery of the glass along a direction of theconcentration difference, the reinforced layer L₃ extends at a ratehigher than that of the reinforced layer L₂, and after full ion exchangereaction, the reinforced layer L₃ is overlapped with the reinforcedlayer L₂, to form a reinforced layer, wherein the time period andtemperature for the second ion exchange process in Step C and the timeperiod and temperature for the thermal processing in Step B satisfyT₂×t₂<T_(h)×(t_(h)/2).
 2. The method according to claim 1, wherein theglass having the reinforced layer L₁ obtained in Step A is taken out,cooled, and rinsed, to remove the ingredient of the molten salt bathadhered to the glass surface in Step A completely, and then the rinsedglass having the reinforced layer L₁ is used in the process of Step B.3. The method according to claim 1, wherein Steps B-C are repeated,until a satisfactory reinforced layer is formed on the glass.
 4. Themethod according to claim 1, wherein the temperature of the molten saltbath is 350-550° C. during the first and second ion exchange process. 5.The method according to claim 1, wherein the glass is alkaline silicateglass comprising: 15-72 wt % of SiO₂; 10-43 wt % of Al₂O₃ or/and P₂O₅ intotal; 8-33 wt % of alkaline metal oxides in total; and less than 15 wt% of other oxides.
 6. The method according to claim 1, wherein a maximumvalue of the refractive index presents at an outermost surface of theglass body, and a difference between the maximum value and therefractive index of the glass body is not higher than 0.1.